1. Field of the Invention
The present invention relates to an electrophotographic image forming apparatus such as a copying machine, a facsimile machine, or a printer.
2. Description of the Related Art
There is known an image forming apparatus as an apparatus in which a toner image formed on a photoconductive drum is transferred to a sheet of recording paper so as to form an image on the sheet of recording paper. Conventionally, an image forming apparatus capable of obtaining high quality printed image is desired.
FIG. 6A and FIG. 6B show part of an image forming apparatus 1 in accordance with the conventional technique. FIG. 6A is a cross sectional view and FIG. 6B shows a simplified model. As shown in FIG. 6A, a photoconductive drum 2 is composed of a hollow cylindrical photoconductive drum elementary pipe portion 43 and a pair of drum flanges 6 which cover openings at both ends of the photoreceptor drum elementary pipe portion 43. Further, a drum shaft 8, which penetrates the photoconductive drum 2 in the axial direction, is provided on the same shaft as that of the photoconductive drum 2. Then, the drum shaft 8 is rotatably supported by a pair of shaft bearings 41 provided at both ends of the drum shaft.
A transfer roller 3 has a cylindrical shape, and an axis A2 thereof is arranged in parallel with an axis A1 of the photoconductive drum 2. Further, a roller shaft 7, which penetrates the transfer roller 3 in the axial direction, is provided on the same shaft as that of the transfer roller 3, and is rotatably supported by a pair of shaft bearings 42 provided at both ends of the roller shaft. Further, the roller shaft 7 comes in contact with a pair of spring members 5 having elasticity in the axial direction, a pair of tracking rolls 4, which are a control means according to the invention, are provided. The roller shaft 7 is pressed against the drum shaft 8 with the spring members 5. The gap H is made between the photoconductive drum 2 and the transfer roller 3 at a proper value by allowing each tracking roll 4 to come in contact with the photoconductive drum 2. Such conventional image forming apparatus 1 is disclosed in Japanese Unexamined Patent Publication JP-A 9-218549 (1997).
Such an image forming apparatus 1 is configured to make the gap between a circumferential surface of the photoconductive drum and a circumferential surface of the transfer roller. Accordingly, the photoconductive drum and the transfer roller can move without friction, so that abrasion and peeling of the photoreceptive layer in the circumferential surface of the photoreceptor drum can be prevented. Consequently, the toner image can be finely transferred to the recording paper, thereby preventing fluctuation of image.
Further, in addition to the above mentioned image forming apparatus which is configured to keep the gap between a circumferential surface of the photoconductive drum and a circumferential surface of the transfer roller at a proper value by the controlling means such as a tracking roll, there is another image forming apparatus, which is configured so as to press the circumferential surface of the photoconductive drum and the circumferential surface of the transfer roller with a specific pressure by the controlling means. Such conventional technique is disclosed in Japanese Unexamined Patent Publication JP-A 2-165173 (1990).
According to the image forming apparatus, by bringing the circumferential surface of the photoconductive drum into contact with the circumferential surface of the transfer roller, and by pressing them at a steady specific pressure, there is no need to further increase the transfer electric field (or potential difference) which functions between the circumferential surface of the photoconductive drum and the circumferential surface of the transfer drum. Further, problems such that letters are missing in the middle part due to high pressure is not raised. Consequently, the toner image can be finely transferred to the recording paper.
The foregoing conventional technique has the following problems, in which the positional relationship between the outer circumference of an image carrier which supports a toner image, such as a photoconductive drum, a photoconductor belt, and an intermediate transfer, and the circumferential surface of the transfer roller which transfers the toner image on the image carrier to the recording paper, is controlled to be a predetermined positional relationship by spring members and the controlling means.
When inserting a sheet of recording paper between the surface of the image carrier and the surface of the transfer roller, the interval between the photoconductive drum and the transfer roller further increases in comparison with the case where sheets of recording paper are not housed in the space between the surface of the image carrier and the surface of the transfer roller. After discharging the recording paper from the space between the surface of image carrier and the surface of the transfer roller, the positional relationship is reset to its original position by the spring members. At the time, an impact caused by insertion and withdrawal of the recording paper, is transmitted to the image carrier. In particular, when inserting a recording paper having a certain thickness and unevenness, the impact is increased.
An impact is transmitted to the image carrier, thereby causing displacement of the image carrier in a short time and creating vibrations on the toner image supported on the image carrier and unfixed toner image which is transferred to the recording paper. Consequently, there is problems that blot and blur of image are generated due to vibrations and high quality image cannot be obtained. In a particular case where the image carrier and the transfer roller have a hollow, when an impact is transmitted to the outer circumference of the portion having a hollow inside, vibrations created by the image carrier is further increased.
Further, according to the copying machine, which is one example of the image forming apparatus, after fixing an image of a developing material such as a toner on the circumferential surface of the photoconductive drum, which is one example of the image carrier, the toner image is transferred to transfer materials such as a transfer sheet, thereby printing the image. At the time, in the periphery of the photoconductive drum, rotating bodies are provided, namely, a charging roller which applies static charges to the photoconductive drum, a developing roller which forms a toner image on the circumferential surface of the photoconductive drum, and a transfer roller which transfers the toner image by pressing against the circumference of the photoconductive drum. At this time, to obtain an image having a certain quality, these rotating bodies provided in the periphery are required to keep the interval between shafts or the interval between circumferential surfaces with regard to the photoconductive drum with high accuracy.
In response to the needs, the following technique is proposed in, for example, JP-A 2-165173 and Japanese Unexamined Patent Publication JP-A 8-63043 (1996). A guide portion is provided on the peripheral rotating body such as the transfer roller and the circumference or the rotation axis of the image carrier such as the photoconductive drum, and the guide portion comes in contact with the circumference of the image carrier or the peripheral rotating body, thereby keeping the interval between shafts of the image carrier and the peripheral rotating body and the interval between the circumferences to a proper value.
Further, according to the technique disclosed in Japanese Unexamined Patent Publication JP-A 4-175779 (1992), a ring-shaped spacer roller provided on the peripheral rotating body are brought into contact with support members of the image carrier, thereby the interval between shafts of the image carrier and the peripheral rotating body and the interval between the circumferences can be kept to a proper value.
In JP-A 2-165173 and JP-A 8-63043, the following technique is disclosed. The guide portion or the like comes in contact with the opposing material while rotating around the periphery of each rotating shaft in accordance with the rotation of the image carrier and the peripheral rotating body. In JP-A 4-175779, the spacer roller are brought in contact with a supporting portion of the image carrier while rotating in accordance with the rotation of the support member of the image carrier and the peripheral rotating body.
Then, in the periphery of the image carrier, fine particles made of the developing material such as a toner, and the transfer material such as a transfer sheet, are suspended in general. In such environment, there is a problem in accordance with the technique disclosed in JP-A 2-165173 and JP-A 8-63043. Because the guide portion comes in contact with the opposing material while rotating, the particles bite the contact surface, thereby creating vibrations on the image carrier and the peripheral rotating body, or causing the abrasion on the contact surface. Consequently, it becomes difficult to keep the interval between the image carrier and the peripheral rotating body to a proper value, in some cases. Further, according to JP-A 4-175779, since the support member of the image carrier to be contacted with the spacer roller is generally charged, it can relieve adhesion of the toner or the like, however, it is impossible to solve the problem of the abrasion. Moreover, the guide portion disclosed in JP-A 2-165173 and JP-A 8-63043, and the spacer roller disclosed in JP-A 4-175779, the whole circumferences become the contact surface. Therefore, there is necessity to process the whole circumferences of the guide portion and the spacer in high accuracy, so that the cost of processing rises.
Further, according to the copying machine, which is one example of the image forming apparatus, to transfer a toner image formed on the circumference of the photoconductive drum (an example of an image carrier), to a paper or the like (an example of a transfer material), the paper is guided to the predetermined transfer position by a paper guide (an example of a guide member) in close proximity to the transfer roller (an example of a transfer member). The paper or the like is pressed against part of the circumferential surface of rotating photoreceptor drum by the transfer roller, thereby transferring the toner image. At the time, to keep a certain image quality of the transferring image transferred to the paper or the like, the transfer roller and the paper guide should be arranged with respect to the photoreceptor drum with high accuracy.
Then, when a paper jam is caused between the transfer roller and the photoreceptor drum or the paper guide, or when a stain is found on the circumferential surface of the transfer roller, it is necessary to remove the jammed paper or perform maintenance such as cleaning of the circumferential surface of the transfer roller. Because of this, the transfer roller and the paper guide, which is formed in close proximity thereto, should be supported to be separated. Also, it is desirable to perform the separation easily. To meet the needs, the following technique is disclosed in Japanese Unexamined Patent Publication JP-A 11-93940 (1999). As a method of supporting the transfer roller so as to facilitate a work top mount and demount, mounting and demounting of the transfer roller can be easily carried out by providing a collar, a handle part, and the like provided with a small-diameter part in a non-circular shape in cross section, at the end portion of the rotation axis of the transfer roller, and rotating the small-diameter part in the direction capable of mounting and demounting through operation of the handle part.
According to JP-A 11-93940, however, when mounting and demounting the transfer roller at the time of performing maintenance, the paper guide should be mounted and demounted with a screw and the like, so that there is a problem that it takes much time to perform maintenance operation. Moreover, there arises another problem that the extent of screwing causes displacement of the positional relationship between the transfer roller and the paper guide.
According to the copying machine and the like, which is one example of the image forming apparatus, to transfer a toner image formed on the circumferential surface of the photoconductive drum (an example of an image carrier), to a paper or the like (an example of a transfer material), the paper is guided to the predetermined transfer position by a paper guide (an example of a guide member) in close proximity to the transfer roller (an example of a transfer member), The paper is pressed against part of the circumferential surface of rotating photoconductive drum by the transfer roller, thereby transferring the toner image. Further, the paper which is stuck to the photoconductive drum due to static electricity, is peeled off by removing static electricity from the transferred paper, with a means for removing static. At the time, to keep a certain image quality of the transferring image transferred to the paper, the interval between the transfer roller or the paper guide and the means for removing static should be arranged with respect to the photoreceptor drum with high accuracy. In addition to this, the intense of pressing the transfer member against the photoconductive drum should be kept consistently.
To meet the needs, the following technique is disclosed in Japanese Examined Patent Publication JP-B2 2710996. By supporting the paper guide with a shaft of the transfer roller, the paper guide is arranged with respect to the transfer roller with high accuracy.
In general, the transfer member such as a transfer roller is pressed against the image carrier with a spring or the like so as to keep consistent intense of pressing against the image carrier. Accordingly, when the surface of the transfer member deteriorates with time, the position of the rotation axis of the transfer member with respect to the image carrier is deviated. At the time, since the paper guide is supported with the shaft of the transfer roller according to JP-B2 2710996, there is a problem that the position of the paper guide with respect to the image carrier is also deviated. Further, when performing maintenance on the transfer roller at paper jam, it is necessary to remove the paper guide from the shaft of the transfer roller. However, the function of facilitating the removal is not indicated, so that there is a problem that maintenance operation is difficult.
Moreover, the function for positioning of the means for removing static electricity is not particularly disclosed in JP-B2 2710996. It can be considered to support the means for removing static electricity with a shaft of the transfer roller, as in the case of supporting the paper guide disclosed in JP-B2 2710996, however, there is a problem that the position is deviated when the surface of the transfer roller deteriorates with time.
It is an object of the invention to provide an image forming apparatus in which fine transfer can be carried out without transmitting vibrations to an image carrier and a recording paper even if an impact is caused when inserting and discharging the recording paper.
It is an object of the invention to provide an image forming apparatus at low cost, in which proper positioning can be carried out without causing vibrations due to a bite of suspended particles such as a toner or the abrasion of the members for positioning.
It is an object of the invention to provide an image forming apparatus in which positioning of the transfer member and the guide member which guides a transfer material to the transfer position, can be carried out with respect to the image carrier with high accuracy, and the guide members, which are arranged in close proximity to the transfer member, can be easily separated so as to perform maintenance on the transfer member.
It is an object of the invention to provide an image forming apparatus which facilitates the positioning of the transfer member, the guide member, the means for removing static electricity, and the like, with respect to the image carrier with high accuracy.
The invention provides an image forming apparatus comprising:
an image carrier for carrying a toner image; and
a transfer roller which is loaded with a force that tends to move the transfer roller toward the image carrier, the transfer roller being arranged in a predetermined positional relation to the image carrier by control means,
wherein the control means is disposed between an axis of the transfer roller and an axis of the image carrier so as to be located outwardly away from an axial end portion of the image carrier.
The invention provides an image forming apparatus comprising:
an image carrier, rotatably supported, for carrying a toner image;
a peripheral rotary body involved in image formation, which is rotatably supported in a periphery of the image carrier; and
control means for controlling displacement of the peripheral rotary body in a direction proximate to the image carrier so as to maintain a predetermined positional relationship between the image carrier and the peripheral rotary body, the control means being so configured that an acting point of impacting force, which is generated in between the image carrier and the peripheral rotary body at a time of image formation, is located on an axis of the image carrier between a position of an axial end portion of the image carrier and a position nearby in which the image carrier is supported.
According to the invention, the image carrier and the peripheral rotary body, for example a transfer roller, are arranged in a predetermined positional relationship by the control means. The control means is arranged axially outwardly relative to the image carrier. This arrangement helps reduce the amount of displacement of the image carrier resulting from impacting force caused by insertion and ejection of a recording paper sheet.
According to the invention, when impacting force is generated due to the passage of the recording paper sheet, the amount of displacement of the image carrier, as well as vibrations developed in the image carrier per se, can be reduced. This makes it possible to prevent a blurred image from occurring at the time of insertion and ejection of a recording paper sheet, thereby obtaining high-quality images.
Besides, in the image forming apparatus embodying the invention, there is no need to increase an axial dimension of the image carrier for the sake of abutment of the control means, and therefore the image carrier can be made small in the axial dimension. This contributes to reduction in cost associated with the image carrier which is consumable yet expensive.
In the invention, it is preferable that the control means is made of a material having shock absorbency.
According to the invention, since the control means is made of a shock-absorbing material, an impact caused by insertion and ejection of a recording paper sheet can be absorbed by the control means, there by alleviating the impact on the image carrier and the recording paper sheet during image transfer process.
Further, according to the invention, the control means is capable of absorbing an impact. Thus, the impact on the image carrier and the recording paper sheet during image transfer process can be further alleviated, thereby attaining more satisfactory image quality.
In the invention, it is preferable that the control means includes a first control member loosely fitted to a shaft of the image carrier and a second control member loosely fitted to a shaft of the peripheral rotary body, the first and second control means abutting against each other.
According to the invention, the first and second control members are loosely fitted to the shafts of the image carrier and the peripheral rotary body, for example, a transfer roller, respectively. In this arrangement, even if the image carrier and the transfer roller are rotated, the first and second control members can be constantly kept at rest in an abutting state without rotating. Consequently, the control members are each inhibited from rotating concurrently with the image carrier and the transfer roller, thereby preventing the wearing away of the abutment surfaces of the control members. Moreover, since the abutment surfaces of the control members are made less prone to adhesion of foreign matters such as toner, a predetermined positional relationship can be established between the image carrier and the transfer roller with high accuracy.
Further, according to the invention, the wearing away of the abutment surfaces of the first and second control members, as well as adhesion of foreign matters, can be successfully prevented, and thereby a certain gap can be secured between the image carrier and the transfer roller with accuracy. This makes it possible to impart steady contact pressure force to a recording paper sheet during image transfer process, thus allowing the toner image to be transferred onto the recording paper sheet without causing unevenness.
In the invention, it is preferable that the control means is arranged outwardly away from the axial end portion of the peripheral rotary body.
According to the invention, the control means is arranged away from the end portion of the peripheral rotary body, for example, a transfer roller. This arrangement helps reduce the amount of displacement of the transfer roller caused by impacting force resulting from insertion and ejection of a recording paper sheet.
Further, according to the invention, since the control means is arranged away from the end portion of the transfer roller, the amount of displacement of the transfer roller caused by impacting force can be reduced. This further decreases the possibility of a blurred image being created during insertion and ejection of a recording paper sheet.
In the invention, it is preferable that the image forming apparatus further comprises oscillation control means for controlling oscillation of each of the first and second control members.
According to the invention, the first and second control members are inhibited from oscillation and kept in an abutting state. Thus, it never occurs that the fine particles are bitten into the abutment portions or that the abutment portions rub and wear. Moreover, by not processing the entire circumferential surfaces of the first and second control members but only their abutment portions with high accuracy, the processing operation can be carried out at relatively low cost.
In the invention, it is preferable that the oscillation control means is so configured as to inhibit rotation of the first and second control members.
According to the invention, the first and second control members can be disposed so as not to rotate in synchronism with the rotary shaft.
In the invention, it is preferable that the abutment portion of the first control member, which abuts against the second control member, is so configured as to protrude outwardly relative to the other non-abutting portions.
According to the invention, the first control member can be made lighter in weight and occupies less space than in a case of adopting a disc shape.
In the invention, it is preferable that a helical gear is additionally provided as driving means for rotatably driving at least one of the image carrier and the peripheral rotary body.
According to the invention, vibrations resulting from a bite of suspended particles such as toner, as well as abrasion of the positioning members, can be successfully prevented. This allows highly accurate positioning of the rotatably-supported image carrier and the peripheral rotary body involved in image formation rotatably arranged in the periphery of the image carrier, such as a charge body or transfer member.
The invention provides an image forming apparatus comprising:
an image carrier for carrying a toner image;
image carrier supporting means for supporting the image carrier in such a way that the image carrier is rotatable about a first rotary shaft which is arranged substantially horizontally;
a transfer member for transferring the toner image carried on the image carrier onto a transfer material;
transfer member supporting means for supporting the transfer member in such a way that the transfer member is rotatable about a second rotary shaft which is arranged substantially parallel to the first rotary shaft; and
a guide member, arranged in close proximity to the transfer member, for guiding the transfer material to a transfer position in the transfer member, the guide member being supported by the transfer member supporting means.
According to the invention, since the guide member is supported by the transfer member supporting means for supporting the transfer member, positioning of the guide member with respect to the transfer member can be achieved with high accuracy. This allows the transfer material to be guided to the transfer position with improved accuracy.
In the invention, it is preferable that the transfer member supporting means and the guide member are each designed to be positioned with respect to the image carrier supporting means by abutting against the image carrier supporting means.
According to the invention, the transfer member supporting means and the guide member can be positioned with respect to the image carrier supporting means with high accuracy. This allows the transfer member and the guide member to be positioned with respect to the image carrier with high accuracy, so that the quality of the transferred image is maintained at a predetermined level.
In the invention, it is preferable that the guide member is supported by the transfer member supporting means so as to be oscillatable within a predetermined range of oscillation, and that, when the transfer member supporting means is moved away from the image carrier supporting means, the guide member oscillates so as to be located in a position distant from the transfer member.
According to the invention, prior to performing maintenance on a path through which the transfer material passes, the transfer member supporting means and the image carrier supporting means are moved away from each other. This allows the guide member to move away from the transfer member, thereby facilitating the maintenance of the transfer position.
According to the invention, the transfer member and the guide member for guiding the transfer material to the transfer position can be positioned with respect to the image carrier with high accuracy. This makes it possible to maintain the quality of the image transferred onto the transfer material at a predetermined level. Moreover, the guide member can be easily moved away from the transfer roller arranged in close proximity thereto, thereby facilitating maintenance such as cleaning of the transfer roller.
The invention provides an image forming apparatus comprising:
an image carrier for carrying a toner image;
image carrier supporting means for supporting the image carrier in such a way that the image carrier is rotatable about a first rotary shaft which is arranged substantially horizontally;
a transfer member for transferring the toner image carried on the image carrier onto a transfer material;
transfer member supporting means for supporting the transfer member in such away that the transfer member is rotatable about a second rotary shaft which is arranged substantially parallel to the first rotary shaft;
a cover member, arranged so as to be freely movable close to and away from the image carrier supporting means, for supporting the transfer member supporting means in such a way that the transfer member supporting means is kept in a floating state in a substantially horizontal direction;
a guide member, arranged in close proximity to the transfer member, for guiding the transfer material to a transfer position in the transfer member;
a transfer member supporting means urging mechanism, disposed in the cover member, for resiliently urging the transfer member supporting means toward the image carrier supporting means; and
first positioning means, disposed in part of the transfer member supporting means, for positioning the transfer member supporting means with respect to the image carrier supporting means by abutting against the image carrier supporting means.
According to the invention, so long as the transfer member supporting means and the image carrier supporting means can be prevented from moving away from each other by the transfer member supporting means urging mechanism, the transfer member supporting means can be positioned with respect to the image carrier supporting means with high accuracy. As a result, the transfer member is positioned with respect to the image carrier with high accuracy.
In the invention, it is preferable that the transfer member supporting means is additionally provided with a transfer member urging mechanism for resiliently urging the transfer member toward the image carrier.
According to the invention, even if, for example, the surface of the transfer member deteriorates with time, by the transfer member urging mechanism, the contact pressure force of the transfer member with respect to the image carrier can be kept constant.
In the invention, it is preferable that a first urging pressure, which is exerted by the transfer member supporting means urging mechanism in a direction of the image carrier supporting means, is set to be greater than a second urging pressure exerted by the transfer member urging mechanism in the same direction.
According to the invention, the transfer member supporting means is prevented from moving away from the image carrier supporting means by a reaction force exerted by the transfer member urging mechanism. At this time, in order to keep these supporting means closer to each other under a state where vibrations take place in the image forming apparatus, the first urging pressure should preferably be set to be 1.5 times or above greater than the second urging pressure.
In the invention, it is preferable that there are additionally provided guide member supporting means for supporting the guide member on the transfer member supporting means; and second positioning means, disposed in part of the guide member, for positioning the guide member with respect to the image carrier supporting means by abutting against the image carrier supporting means.
According to the invention, the guide member is supported by the transfer member supporting means which is arranged in a predetermined position with respect to the image carrier supporting means. Thus, similarly, the guide member is positioned with respect to the image carrier with a predetermined distance secured therebetween.
In the invention, it is preferable that an urging position in the transfer member supporting means urging mechanism is located in between the first positioning means and the second positioning means.
According to the invention, it never occurs that the urging pressure of the transfer member supporting means urging mechanism is lopsidedly exerted on one of the first and second positioning means, thereby making the positioning state more stable.
In the invention, it is preferable that there is provided charge removal means for removing charges remaining on the transfer material after the transfer process, and the charge removal means is supported by the transfer member supporting means.
According to the invention, the charge removal means is supported by the transfer member supporting means which is arranged in a predetermined position with respect to the image carrier supporting means. Thus, similarly, the charge removal means can be positioned with respect to the image carrier with a predetermined distance secured therebetween.
According to the invention, the transfer member, the guide member, the charge removal means, and the like can be easily positioned with respect to the image carrier with high accuracy, thereby keeping the quality of the image transferred onto the transfer material at a predetermined level.